This invention relates to a blue light emitting display element and more particularly to a blue light emitting display element with a hetero p-n junction suited for emission of light by injection of only a small amount of carriers and their recombination.
Need for blue light emitting diodes has been well recognized but there is yet no commercially available blue light emitting diode with high efficiency which can be mass-produced. Elements having only a p-n junction of SiC and blue light emitting diodes with MIS diode structure by MIS junction of GaN have been successfully developed but light emission efficiency is low with both. Mass-producibility is particularly poor with the former and neither has enjoyed wide commercial acceptance.
In general, it is difficult to produce single crystals and junctions with SiC because its single crystals are difficult to grow and its melting point is high. It is of an indirect transition type and its light emission efficiency is less than 0.1%. As for GaN, only n-type conductive crystals can generally be produced and p-n junctions with which high light emission efficiency may be anticipated cannot be formed. For this reason, MIS diode structures are used with GaN but the light emission efficiency is equally low.
Although several semiconductors with a wide energy bandgap are found among II-VI semiconducting compounds such as ZnS, ZnSe and ZnO and III-V semiconducting compounds such as GaN, AlN and AlP, it is difficult by adding a dopant to produce a semiconductor which can be both p and n type. A small number of carriers are injected by tunnel effect in an MIS structure but the problem of low light emission efficiency still remains as a result.